1. Field of the Invention
The present invention relates to a failure detecting device for a fuel injection control unit of, for example, a multi-cylinder V-type internal combustion engine. If a fuel injection control unit is out of order due to locking (freezing) or the like, since fuel is suppliable to an engine, danger of fire or the like occurs. In addition, since it becomes impossible to actuate an engine at the time of disconnection, detection of a failure is necessary.
2. Description of the Related Art
A conventional failure detecting device will be described with reference to a drawing. FIG. 8 is a diagram showing a structure of the conventional failure detecting device.
In FIG. 8, reference numeral 1 denotes a battery (power supply: e.g., 12V); 2, a relay having an excitation coil and a contact; 3, an ECU (Electronic Control Unit); and 4, an injector. In addition, reference numeral 31 denotes a transistor (TR); 32 and 33, resistances for dividing a voltage (power supply monitor); 34, a microcomputer (arithmetic unit); and 35, a transistor. Moreover, reference numeral 341 denotes an EEPROM (memory device).
Next, operations of the conventional failure detecting device will be described with reference to drawings.
In order to judge return from a failure without wrong detection, it is necessary to store two kinds of information, “presence or absence of a failure” and “state of a failure”, in the EEPROM (memory device) 341.
FIG. 9 is a timing chart showing basic operations of the failure detecting device.
The transistor (TR) 31 of FIG. 8 is ON for a fixed time simultaneously with application of a power supply of the ECU 3 and drives the relay 2. As indicated by (c) in FIG. 9, the transistor 31 is turned OFF after the fixed time has elapsed. In addition, as indicated by (b) and (c) in FIG. 9, when a rotation signal of an engine is inputted (not shown) and the microcomputer 34 judges that the engine is in operation, the microcomputer 34 turns ON the transistor 31 again and drives the relay 2. When the engine stops, the microcomputer 34 turns OFF the transistor 31. If a circuit is normal, variation of a voltage occurs in the power supply monitor (a connection point of the resistances 32 and 33) in association with the operation of the transistor 31. In the case of the above operation state, the relay 2 and a peripheral circuit are in a normal state.
FIG. 10 is a timing chart showing detection of locking and a return logic of the conventional failure detecting device.
As indicated by (d) in FIG. 10, when the relay 2 is locked, the power supply monitor continues to be in an ON state. When an engine rotation signal disappears and the microcomputer 34 judges that the engine has stopped, the microcomputer 34 turns OFF the transistor 31. However, since the relay 2 is locked, the power supply monitor is not turned OFF.
When this state continues for a predetermined time (locking judgment time), the microcomputer 34 judges that locking has occurred. When the engine is actuated again, the transistor 31 is turned ON and the power supply monitor is ON. Thus, the microcomputer 34 can judge the failure detecting device is in the normal state. However, since the failure detecting device is out of order due to locking, the microcomputer 34 does not return the failure detecting device to normal because returning the failure detecting device to normal according to ON of the transistor 31 and ON of the power supply monitor leads to misjudgment.
As shown in FIG. 10, when the engine is stopped again, the transistor 31 is turned OFF and the power supply monitor is turned OFF, the microcomputer 34 judges that the failure detecting device has returned to normal after a predetermined time (return judgment time).
FIG. 11 is a timing chart showing detection of disconnection and a return logic of the conventional failure detecting device.
As indicated by (d) in FIG. 11, when the peripheral circuit of the relay 2 is disconnected, the power supply monitor continues to be in an OFF state. When the peripheral circuit of the relay 2 is disconnected during operation of the engine, the power supply monitor is turned OFF. When this state continues for a predetermined time (disconnection judgement time), the microcomputer 34 judges that disconnection has occurred.
When the engine stops and the transistor 31 is turned OFF, the microcomputer 34 can judge that the failure detecting device is normal according to OFF of the transistor 31 and OFF of the power supply monitor. However, since the failure detecting device is out of order due to disconnection, the microcomputer 34 does not return it to normal because returning it to normal in this state leads to misjudgment.
As shown in FIG. 11, when the engine operates again, the transistor 31 is turned ON and the power supply monitor continues to be ON for a predetermined time (return judgment time), the microcomputer 34 judges that the failure detecting device has returned to normal.
FIG. 12 is a timing chart showing operations at the time when the conventional failure detecting device is turned OFF in a disconnection state. In addition, FIG. 13 is a timing chart showing operations at the time when the conventional failure detecting device is turned OFF in a locked state.
As described in FIGS. 10 and 11, it is necessary to hold a failure state in order not to mistake judgment of return from a failure. This means that it is necessary to also hold the failure state continuously when the power supply of the ECU 3 changes from ON to OFF to ON.
FIG. 12 is a timing chart showing operations for holding a disconnection failure at the time when the power supply is turned OFF in a disconnection state and is turned ON again. After the peripheral circuit of the relay 2 is disconnected and a disconnection judgment is established, when a failure occurs or when the power supply of the ECU 3 is turned OFF, the microprocessor 34 causes the EEPROM 341 (memory device) to store information indicating presence or absence of a failure (failure detection flag) and information indicating that the failure detecting device is out of order in a disconnection state (disconnection failure flag).
The microcomputer 34 reads out these information from the EEPROM 341 when the power supply of the ECU 3 is applied again and holds the state. This operation is represented by flow charts as shown in FIGS. 14 and 15.
That is, as shown in FIG. 15, in step 400, upon detecting that the power supply is turned OFF, the microcomputer 34 stores the failure detection flag, the disconnection failure flag and the locking failure flag in the EEPROM 341.
In addition, as shown in FIG. 14, in step 300, upon detecting that the power supply is turned ON, the microcomputer 34 reads out the failure detection flag, the disconnection failure flag and the locking failure flag from the EEPROM 341.
FIG. 13 is a flow chart showing operations for holding a locking failure at the time when the power supply is turned OFF in a locked state and is turned ON again. As in FIG. 12, the microcomputer 34 stores information on the failure in the EEPROM 341 at the time of locking and takes out the information on the failure at the time when the power supply of the ECU 3 is applied again.
FIGS. 16 and 17 are timing charts showing operations of return judgment at the time when the failure detecting device is repaired from the respective failure states.
FIG. 16 is a timing chart showing operations at the time when a disconnection failure is repaired and the failure detecting device returns from the disconnection state. When the ECU 3 is operated by applying the power supply again and the transistor 31 is ON for a fixed time, since the repair is completed, the power supply monitor is also turned ON. When this state continues for a predetermined time (return judgment time), the microcomputer 34 judges that the failure detecting device has returned to normal. Usually, since ON time of the transistor 31 at the start of operations of the ECU 3 is longer than a predetermined time for return judgment, return judgment ends when the power supply is applied.
FIG. 17 is a timing chart showing operations when a locking failure is repaired and the failure detecting device returns from the locked state. After the ECU 3 is operated by applying the power source again and the transistor 31 is ON for a fixed time, the transistor 31 is turned OFF. At this point, since the repair is completed, the power supply monitor is also turned OFF. When this state continues for a predetermined time (return judgment time), the microcomputer 34 judges that the failure detecting device has returned to normal. In addition, if the engine comes to be in an operation state within a fixed time after the operation of the ECU 3, when the transistor 31 is turned OFF after the engine stops, normal return judgment becomes possible and the failure detecting device returns to normal.
In storing information in a memory device, a mechanism and/or a contrivance is required taking into account an amount of information of the memory device and reliability of the memory device, which increases loads and costs for a system.
For example, in recording information in an EEPROM, in order to prevent miswriting in such a case in which a failure of the EEPROM or power OFF occurs concurrently with writing in the EEPROM, countermeasures for a power supply circuit and a logic for judging miswriting are required, which makes processing complicated and increases loads applied to software. The increase of loads applied to software leads to increase in a program size, verification items of the software and the like.